As optical networks support communications including burgeoning Internet traffic, the need for advanced and efficient optical components rises. Optical communication systems permit the transmission of large quantities of information. Improved optical integrated circuits (OICs) are particularly needed. OICs come in many forms such as 1×N optical splitters, optical switches, wavelength division multiplexers (WDMs), demultiplexers, optical add/drop multiplexers (OADMs), and the like. Optical circuits allow branching, coupling, switching, separating, multiplexing and demultiplexing of optical signals without intermediate transformation between optical and electrical media.
Such optical circuits include planar lightwave circuits (PLCs) having optical waveguides on flat rectangular substrates, which can be used for routing optical signals from one of a number of input optical fibers to any one of a number of output optical fibers or optical circuitry. PLCs make it possible to achieve higher densities, greater production volume and more diverse functions than are available with fiber components through employment of manufacturing techniques typically associated with the semiconductor industry. For instance, PLCs contain optical paths known as waveguides formed on a silicon wafer substrate, wherein the waveguides are made from transmissive media which have a higher refractive index than the chip substrate or the outlying cladding layers in order to guide light along the optical path. PLCs are fashioned to integrate multiple components and functionalities into a single optical chip.
One important application of PLCs specifically and OICs generally involves wavelength-division multiplexing (WDM) including dense wavelength-division multiplexing (DWDM). DWDM allows optical signals of different wavelengths, each carrying separate information, to be transmitted via a single optical channel or fiber in an optical network. In order to provide advanced multiplexing and demultiplexing (e.g., DWDM) and other functions in such networks, arrayed-waveguide gratings (AWGs) are available in the form of PLCs. These applications, especially AWG's, however, are extremely sensitive to temperature variations and stress including thermal stress. Consequently, devices used in these applications often suffer from thermal stress induced birefringence and resultant polarization dependent wavelength shift